Apparatus for producing hyperpure gallium



Feb. 23, 1965 s. LEIBENZEDER APPARATUS FOR PRODUCING HYPERPURE GALLIUMOriginal Filed Sept. 28, 1961 3,170,861 APPARATUS FOR PRODUCINGHYPERPURE GALLIUM Siegfried Leibenzeder, Erlangen, Germany, assignor toSiemens Schuckertwerke Aktiengesellschaft, Berlin- Siemensstadt andErlangen, Germany, a corporation of Germany Original application Sept.28', man-sea No. 141,381.

Divided and this application May 6, 1964, Ser. No.

370,749 H I Claims priority, applicgtlgaaGgrmanyfsept. 30, 1960,

y 1 Claim., (Cl. got- 239 i p This applicationiisa division ofapplication Serial No. 141,381,, filed September. 23 1961.

{ 'My-invention'relates"to apparatus for the productiori'oi hyperpuregallium, su'ch'asf'required for the production of electronicsemiconductors from gallium compounds, for example, GaP, GaA s, GaSb','or 'as required foruse as doping or contact substance for semiconductorbodies.

' Hyperpure gallium is also used, for example, in high temperaturethermometers and as a metallic heat-exgchange liquid in cooling systems.

Various methods have become known for extreme puri tion of galliumbromide complex. Commercially'aval ficationof gallium} Pastinvestigations have mainly been directed to refinement'of gallium byelectrolytic processes. Among the. known refining methods are theprecipitation from aqueous medium, as well as the molten-bathelectrolysis. The first-mentioned method has only a slightpurifyingefiect, .in contrast to molten-bath. electrolysis which affordsa high purity of the separated gallium, this purity'beingdependent-1o agreat extent upon accurate control of electric-potentials; It is anobject of my invention to devise a method and apparatus for the"production of hyperpure gallium on electrolytic principles in which therefining action is independent, within a wide range, of accuratelyconstant potentials and, under otherwise comparable conditions, permitsa considerable increase in' yield'by operation atincreased"electrolyticlcell voltages. V

To achieve these objects and accordancewith my invention, I employ aselectrolyte for electrolytic precipitation, the solution of a gallium,complex'of, the type Ga(GaX in a non-aqueous organicsolvent, wherein Xdenotes a halogen element, which as used herein is understood to bechlorine, bromine and 'iodine. Particularly suitable as the non-aqueousorganic solvent are benzene, toluene and xylene, and as galliumcomplexes are G'a(GaCl Ga(GaBr )and Ga(GaI over the just-mentioned knownmethods, namely the'fact that the purifying action-does not depend uponthe separation potential so that relatively high cell voltages can beused and a highly purified gallium is readily obtained with a singleseparation process, satisfying toa great extent the exact impurityrequirements of electronic semiconductor techniques. 7

The invention involves the observation that the gallium complexes of theabove-mentioned type possess good solubility as Well as electricconductivity in non-aqueous 3,170,861 I P nt Feb. 33,1965

Ice

Ga(GaB r in benzene; at 20 l C. is approximately 1200 g./li ter, and isonly .slightlyless than the solubility in toluene and xylene. Thespecific electric conductivities S in ohm-l cm. ).;of the electrolytesused according to; the invention is indicated in the following Table l.

\ Table'l V 3 1 I Qoneen ,tration in 1 percent by ,Anotherivadvantageover:the methods heretofore known resides in, the production oftliel'ectrolyte. Theprepafaa tion of-the gallium complex-{to be employedaecording to the invention is efieeted in known manner through thereduction of GaX (wherein X -denotes a halogen element) with'gallium inaccordance. withthe following reexample of the technique is given' bytainingfthehighpurifying action apparent 'frorn-Table'li t Table- 2Concentration Concentrationof I p of the foreign the foreign eleelementsof the "merits-of the 1 Element anodic Gain catho'dieally pre p.p.m.(10- eipitatedGa in percent) 1 p.p .m (10- percent) '491 10. H H a 3.3Not detectable. 2.4 Do.

By asecond refining operation,--the purir' yi ilgeffect-can aromaticorganic solvents, for example benzene, toluene and xylene, and that theuse otsuch solutions as an "electrolyte results in the precipitation ofgallium. This was all the lessexpectable as :the above-mentionedcomplexes have a salt-like structure.

In fact, however, it has beenfound that, for example, a solubility ofGa(GaCl and begstill furtherincreased to a considerable extent, as apparenttromTable 1.; i f.

As 'isfurther apparent from the apparatus described hereinafter, theabove-mentioned extreme purity of the refined product is obtained withthe minimum in equipment and with a good yield per unit of time.

When performing the method according to my invention, it is significantthat no gas development occurs during the-electrolysis so thattheprocess can'be carried out in a completely closed vessel. Thisexcludes the danger of contamination from the ambient atmosphere. In theelectrolytic cells, the contamination can also be avoided to a greatextent because the electrolysis can be performed at a temperature ofabout 50 C. and the electrolyte is only slightly aggressive.

To further describe the invention, reference is made to the drawing andthe specific example hereinbelow.

The drawing shows a schematic and sectional view'of an electrolysisdevice for performing the above-described method. The anode is formed bymolten gallium located at 1 on the bottom of the electrolytic cell.Current is supplied to the anode by a platinum wire 2 which is immersedat its lower end into the molten gallium. The cathode is denoted by 3and a collector funnel by 4. The funnel 4 is connected with a receivingvessel 5 through a 14. Simultaneously, the condensers and 12 are putinto operation, the anode current supply lead 2 is inserted, thusclosing the opening of the nipple 17, and the cathode 3 is insertedthrough nipple 20. A voltage of from about to about v. is applied to thecell between cathode and anode. This results in the flow of an averagecurrent value of about 0.4 amp. Precipitation of about 1 g./hour ofhyper-pure gallium takes place with a current yield of about 100%.

Aside'from the addition of the anode gallium and the removal of thecathodically precipitated gallium, the device operates practicallyautomatically, continuously and free of maintenance over a long periodof time.- After starting the process, the platinum wire of the cathodebecomes coated with gallium melt, until a drop of gallium is formed atthe lower end and drips into the collecting funnel 4. v This is repeatedcontinually.

The precipitation is preferably carried out with a high a cathodecurrent density which preferably should not capillary fi. Theelectrolyte 7 covers the anode 1 and i forms-part of a thermosiphonsystem which serves to maintain the electrolyte in circulation. Thissystem comprises the two legs 8 and 9 which are interconnected bytransverse portion 13. 'Leg 9 is surrounded by a cooler 10. Leg 8 hasits lowerend widened to form an inverted funnel portion at 11 abovethecathode 3 and in upwardlyspaced relation to the funnel 4. Connected tothe circulation system of the electrolyte is a reflux condenser 12. Thesuction nipple of the reflux condenser 12 is denoted by 14. To preventcontamination, the nipple 14 is closed by a protective cover 15 duringoperation of the device.' A stop-cock is provided at 16. The cell vesselis further provided at 17 withaconical ground nipple through which theanode current-supply lead enters into the vessel. The nipple 17 alsoserves to supply the vessel with electrolyte. The receiving vessel 5 forthe purified gallium 19 is sealed by a stoppered ground nipple 18.Conically ground junctions at 21 connect the lower portion of.theelectrolytic cell with the upper portion thatcontains theabove-described entire electrolyte-circulating system.

- The quantity of cathode gallium required for starting the process issupplied through the receiving vessel 5 so that the capillary 6 and thereceiving funnel 4 are filled with gallium. The anode gallium 1 issupplied through the central nipple 17 in a quantity sufficient to bringthe level of the anode gallium to a height of at most a few millimetersbelow the lower end of the tube 9. Thereafter, the electrolyte is filledinto the vessel through the same nipple 17. Since the electrolytemustnot be subjected to moisture, the filling must be done in a sealedcontainer through a siphon or pump with the aid of a dry inert gas, forexample, nitrogen. The electrolyte, for exbe below 200amperes/de'cimeter This is aided by the fact that the cathode surface isvery small in comparison with the anode surface.

However, if the cathode current density is considerably lowered belowthe above-mentioned amount, then, according to another embodiment of theinvention, the

gallium becomes precipitated as a fine pulverulent metal.

ample, is composed of 50% by weight of Ga(GaBr and This powder issuitable, for example, for the production of gallium containingsemiconducting sinter materials,

which have been recently employed for thermoelectric purposes. 7

The performance of the electrolyte circulation system involvesthethermosiphon principle. That is, the electrolyte heated by theheating bath rises in the leg 8 and passes through the cooled leg 9 backto the lower portion i loules heat which occurs in the vicinity of thecathode in the electrolyte is advantageously used to amplify thethermosiphon effect.

The circulatory system prevents the occurrence of a solid bottom body ofGa(GaX on top of the anode gallium. Such a body would considerablyincrease the ohmic resistance of the cell and, for the same cellvoltage, would result in a reduction of the current density.

' I claim? Apparatus for producing hyperpure gallium for electronicpurposes by electrolytic precipitation, which comprises a closed vesselhaving a gallium anode, a cathode,

a collecting funnel, and a thermosiphon circulatory system, said cathodebeing located above said funnel so that hyperpure galliumelectrolytically precipitating on said cathode drops into said funnel,said thermosiphon system comprising two interconnected inlet and outletlegs, said inlet leg being located above said cathode and said outletleg being located above said anode at a location removed from saidcathode, said outlet leg having cooling means in conjunction therewith.

No references cited.

JOHN H. MACK, Primary Examiner,

